static TripleWebWithSourceAndResult ai_parseQuad(S s) {
  L<S> l = map tok_unCurlyBracket(splitAtSimpleArrow(tok_combineCurlyBrackets_keep(javaTok(s))));
  if (l(l) != 4) null;
  TripleWebWithSourceAndResult w = new(null, l.get(3));
  w.a = l.get(0);
  w.b = l.get(1);
  w.c = l.get(2);
  ret w;
}